It doesn't answer the medium format part of the question, but there is a cheap solution to 35mm, and that's the lowly Pacific Image Prime Film scanners. I've run the gamut of scanners, from Pacific Image to a Hasselblad X1. You certainly get what you pay for, but the humble Pacific Image punches above its weight for relatively little cash. I keep one around (off the top of my head I think the model was 3650u) as an ultimate fallback for when I run out of old Macs to operate the X1, and the Nikon 9000 dies like my KonicaMinoltas did. A flatbed scanner does a good enough job on larger negatives so that's probably the cheap solution for 120 film.